1. Field of the Invention
The invention relates to the field of aircraft radar signature verifying and, in particular, to a method of verifying the radar signature of an aircraft in flight.
2. Description of Related Art
Stealth aircraft typically incorporate shaping of the external contours radar-absorbing structures and radar absorbing coatings. Maintaining the integrity of the system treatments is critical to the survivability of the aircraft. It is also critical that the doors and access panels remain tightly closed for any gaps can significantly increase the radar signature. Thus periodic testing of the aircraft's radar signature is critical, especially if the aircraft is venturing in harms way.
One of the prominent prior art methods is to use a dedicated aircraft to measure the target aircraft's radar signature. This aircraft typically caries a large measurement radar system that transmits from both the front and rear ends of the aircraft. Data collection on a single aircraft can require up to three hours of uninterrupted flight time. The resulting data set is radar images that can only be interpreted by trained engineers. To produce this measurement, the radar aircraft flies a pattern behind the measured aircraft to achieve rear aspect data; and then the measured aircraft flies the same pattern behind the radar aircraft to complete the front aspect data set. In this manner a 360-degree radar image of the measured aircraft is created. Flights are specifically dedicated for measuring tests. Thus individual mission costs can range up to hundreds of thousands of dollars per flight when the cost of operating both aircraft is totaled.
Signature verification is also carried out with dedicated ground-to-air measurement facilities. Aircraft fly controlled patterns around a fixed installation site to develop a sparse azimuthal signature of the measured aircraft. Flights are specifically for signature measurements, therefore all costs are directly related to the measurement process. Unlike the airborne imaging system, these facilities generally can only identify the magnitude of the signature faults and not their locations on the vehicle.
Ground to ground measurements using semi-portable signature verification systems are in use. However, with the landing gear doors open and the gears extended, special radar absorbing structures must be placed thereabout to insure that the they do not interfere with the measurements. In addition, the target aircraft's close proximity to the ground and surrounding structures may introduce radar reflections that can mask the true signature of the aircraft.
Even if these systems were cost effective and/or accurate, there would still be a significant problem. Aircraft in the field are subject to the day to day strains of aircraft flight and constant maintenance. Thus damage to the radar absorption coatings and structures can occur. Equipment access panels and doors may, while secured from a safety standpoint, may not be secure enough so as to effect radar signature. After takeoff, landing gear doors may not close tight or in-flight loads may change rigging tolerances. Thus what is needed is an in flight testing procedure that can be used during the actual mission.
Thus, it is a primary object of the invention to provide a radar signature verification system that can be carried on board the aircraft.
It is another primary object of the invention to provide a radar signature verification system that can be carried on board the aircraft and used during a mission to determine the radar signature of the aircraft just prior to entering combat.
It is a further object of the invention to provide a radar signature verification system that can be carried on board the aircraft that can located the position of any deficiencies in the radar signature of the aircraft.